The invention relates to a solar cell and to a method for manufacturing a solar cell.
An Emitter-Wrap-Through (EWT) solar cell does not comprise any metallization at the front. The emitter is conducted to the cell back by way of a multitude of small holes (d<100 μm) and is contacted at the cell back. The light-generated current is conducted, by way of the emitter and the holes, to contacts that are arranged on said cell back and is tapped there.
The extent of emitter doping plays an important part. Higher doping results on the one hand in lower layer resistance and thus contributes to a reduction in ohmic losses. Furthermore, the contact resistance between the emitter and the metallization is significantly reduced with high emitter doping. High doping on the other hand reduces the ability of the cell to convert in particular shortwave light into current (so-called blue-sensitivity). Accordingly, a compromise between good conductivity and blue-sensitivity must be selected for doping.
In order to reduce the effective layer resistance of an EWT solar cell it is known, for example, from US 2005/0176164 A1 to carry out higher doping in the interior wall of the holes of the cell than on the front of the cell. Such a concept is also referred to as a selective emitter or selective doping. From US 2005/0176164 A1 it is furthermore known (FIG. 3D of this printed publication), at the front of an EWT solar cell, to form a highly doped strip that comprises several of the holes.
U.S. Pat. No. 7,144,751 B1 describes a solar cell in which there is higher doping in the interior wall of the holes of the solar cell and along a grid at the front of the solar cell.
It is the object of the present invention to provide a solar cell with low effective layer resistance while at the same time featuring high blue-sensitivity, and to provide a method for manufacturing such a solar cell.